First Grímsvötn volcano erupted through a glacier. Then it exploded through the air. Finally, its debris changed the atmosphere so much that it blasted winter away from most of the US.

Most people don’t even know anything about Grímsvötn. It blew up in the middle of Iceland last May. Ash and chemicals roared 12 miles high into the air. Then everyone discovered that its ash was too high to mess with air travel to Europe and forgot about it. Unfortunately, the ash and chemicals are still lingering in the air, even if no one cares. They block out sunlight in parts of the Arctic. The air cools. Air pressures change.

What has happened is as simple as 1, 2, and 3.

Winds really make a difference in winter. They can blow Arctic air deep into North America or away from the US.

Air pressure determines where the winds blow. In the North Atlantic, the low pressure near Iceland (called the Icelandic low) steers the winds.

The volcano in Iceland changed the air pressure over Iceland. The Icelandic low became very low.

Last week’s blog The NAO: The Crossing Guard of the Atlantic discussed a weather pattern called the North Atlantic Oscillation (NAO). When the cold Icelandic low is very different from the warm high air pressure in the mid-Atlantic, the Azores High, winds trap the cold Arctic air in the north. This is called a positive NAO and this winter the NAO was more positive than it has been in a century.

The Icelandic Low is so strong that it has created a positive NAO. Source: NOAA

Even now, the NAO is shifting between neutral and positive. It sometimes allows cold air to hit the US, and then it zips it out into the Atlantic. The cold doesn’t stay very long.

It doesn’t mean that it doesn’t get cold. A huge storm from Siberia, “The Beast from the East”, has hit Europe. China has shivered with temperatures below normal since January. Two cold spells plunged down and killed people in India.

Still the cold winter has avoided most of the US. The blast of Grímsvötn, a volcano in Iceland, has warped the normal Arctic winds. In the process, it warmed the US. If you are seeing flowers in February, point to the volcano!

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Evelyn Browning Garriss, historical climatologist, blogger, writer for The Old Farmer's Almanac, and editor of The Browning Newsletter, has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.

Comments

Okay I guess you just answered my question about why the OFA was so far off base with winter weather this year. I live in the Northeast and it said it was going to be below normal temps and more snow and I'm telling you it is as if we haven't had any winter at all. I like it but how could you be so far off? I guess it's the volcano, okay, you're off the hook, this time.

By Maximum Advocate

By denise seamster

Since this winter was a strong la nina year what does that mean for summer if it sticks around with us during the spring? I hope this summer will be really hot because im a big fan of the hot summer days! I heard next winter will be an el nino year most likely. Which is the opposite and el ninos tend to force the jet stream down right? Which would mean next winter might be a different story.... Hopefully :)

By ebgarriss@comcast.net

The NAO shaped by the Icelandic Low kept the Arctic air from entering the Atlantic. It had to go somewhere, so it went into Siberia. As more polar air poured in, the cold expanded through Russia, Eastern Europe and finally into England and France. Normally winter storms hit Europe from the Atlantic. They called this winter of Siberian cold "The Beast from the East."

There are clues that this summer might also be very hot, but it depends on a number of factors that are still changing.

By purrdog

I live in north Texas and our Winter has been warmer and wetter than normal. After the hottest driest summer of 2011 we welcomed the moisture. Out temps,however, have been on somewhat of a roller coaster.

By Been Burned in 2011

No winter here. Golfers love it. I'm in central Texas and 2011 summer was beyond brutal. Will this volcano make it as hot or even hotter this year? Please, no more rolling black outs, wells going dry, fires and vanishing lakes.

By ebgarriss@comcast.net

By mra823

In Endwell, NY which is in upstate New York, we had a very unusually warm winter. Last year, we had a blizzard practicly, dumping over 2 feet of snow. This year, we barely had enough snow to cover the grass.

By kathy dyment

By Aaron Ginther

I live in central Virginia and this was quite mild of a winter. The volcano eruption didnt change the USA weather patterns perminately did it? I sure hope not! That worries me that next winter will be warm too. I love winter and this winter has been miserable. We cant even ski this year. Its been too mild of a winter. Never seen a winter like this

By ebgarriss@comcast.net

By Rachel Hamilton

I live in Utah, near Salt Lake City and I personally have enjoyed a very warm winter with very little snow. I am sure the ski/snow sport industry doesn't love this weather, but being someone origionally from San Diego, I appreciate a break in the winter time. Luckily the past few winters have been wet so we aren't hurting for too much moisture, so for now, I'll happily wait for spring in the not too terrible winter.

By ROBERT C. MCNAIR

We in Fl have had unusally warm winter to the point of flabgastering our weather reporters. It seems we have not had a winter at all in FL.Praying that the summer will not be a swelter and hi-hurricane season. God bless the midwest with their spring storms.

By ebgarriss@comcast.net

It looks like it will be hot, but there is some good news. Scientists are saying that there is a 1-in-3 chance of a warm El Nino developing this autumn. That would really quiet down the hurricane season.

By Jen2012

I am near St. Louis - this winter has been very strange. We have had more thunderstorms than snow all winter long, including tornadoes. Do you think the tornadoes will slow down for us this year in the midwest?